Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
Conventionally, III-nitride devices are grown on a sapphire substrate by MOCVD. However, due to differences in lattice constant and coefficient of thermal expansion between the sapphire substrate and the III-nitride semiconductor material, defects are formed in the semiconductor during growth, which may limit the efficiency of III-nitride devices. Other substrates have been explored in an attempt to alleviate problems associated with growth on sapphire. For example, U.S. Pat. No. 7,173,286 describes “depositing III-nitride compounds on lithium niobate and/or lithium tantalate substrates”.